Abstract - Leveillula taurica (Lev) Am: axenic cultures, biology and parasitic specificity. L taurica is distinguished from the other powdery mildews by the following : - Conservation of isolates is carried out on detached leaves (not on cotyledons) maintained on agar medium (100% relative humidity) on which the spores are deposited in a drop of water on the lower side of the blade (table I). For young tomato leaves, indole butyric acid (1 mg/l) should be added to the medium to prevent foliar necrosis (table II). - The spores germinate very well in liquid medium. Several fungicides have been tested under these conditions: even at high concentrations, none of them have proved to be really efficient (table III). - A special microscopic technique has shown that the germinative tubes enter via stomata (fig 1). However, they seem to play a minor role in contamination. For artificial contamination in the greenhouse, the plants are sprayed with liquid inoculum. It is not necessary to place the material in a damp chamber. The results obtained from cross-infections (4 isolates used on 5 host plants) suggest that there is no parasitic specificity (table IV). The different characteristics noted above are discussed.